TRY AT YOUR OWN RISK. - SHARING THIS TO HELP OTHERS......
If you locate pin 25, which is one of the 2 yellow wires with black tracer, on the top, white wiring harness that plugs in behind the glove box. You can remove the wire from the harness, (so that you can put it back later if you really want to get stuck...) This interupts the signal going to the TRAC module. The TRAC system then operates in 4L. There is no throttle intervention, and it is the best limited slip effect that I have ever experienced. (this is my 5th truck..) The guy who did all the testing found it to perform as well as ATRAC, it is likely the same thing.
This is not my invention, a guy on another Tacoma site tried and quite thoroughly tested this. I cannot guarantee that you won't screw up your truck, but it sure works.

It is the very top yellow wire, it does make a difference! You will know it works if you switch to 4L, and the Traction control light DOES NOT turn on.
This causes the 4L lamp to flash, even once the gears are fully meshed, because this is the signal wire.....

This belongs in technical chat. Post pics of the mod you have done and post up schematics of the systems affected. This will help those that want to do it but are skeptical. At least with a electrical schematic from the Tacoma's FSM you can clearly show what you are doing why you are doing it and how it works. Pictures will illustrate where the connectors are and how they are positioned and where the wire is you are talking about. With any mod you do to your truck/car it definitely comes with a "Try at your own risk".

I went out wheeling for about 4-5 hours this weekend. Obstacles that got me completely stopped and stuck before, I could get over. At one point I was completly stuck in a mudhole, 2nd gear, 4L, and the one front tire that had solid ground pulled me out! It IS NOT as effective as ATRAC, it functions as the 4H TRAC system does. I have 4 videos, they are terrible quality, they are also situations that I caused, with TRAC off, and dug myself in, the first on is contrived, as I dug myself in, 2 wheels airborne. The second, I just drove up an incline, no TRAC, until the truck ROLLED BACKWARDS.
The system acts like a limited slip on both ends. ATRAC is closer to an electronic locker, much tighter, less revving. I was just learning this system, and was using 1st gear, it works, but 2nd @2000-2500 is the sweet spot. Again the vids are bad, sorry, but it's from a phone with the wife recording. There were about 20 real, previously not even close to climbable mud / sand obstacles, now doable. The crowd watching was very impressed. Personally this is the most satisfying mod I have ever done.
Functionaly, it operates, and feels the same if I switch to 4H. TRAC light flashes.....
*******Going to have to work on posting the vids, patience please...

Been looking at this mod for a while now and tried it today. I cut the wire and wired in a switch so I could return it to normal if need be. It seems to work, although it is not atrac, more like TRAC to the front and rear while in 4wd. I think somehow it tells the system it is not in 4wd and the trac system (which is usually disabled in 4wd) is activated.

After watching videos of ATRAC, this is not the same. You don't crawl along like ATRAC. When the wheels without traction start to spin, you give it some extra gas, and the brakes are applied to the spinning wheels and then you start to creep forward. It does let the spin, but i guess when they spin a certain speed, the trac cuts in and brakes those wheels. Will definitely get you out if stuck.

Don't all 2009 and newer 4x4 tacoma's have A-trac? And isnt supposed to work in 4 lo anyway? Or is it an option? I thought I had seen some TRD off road package tacoma's with the A-Trac button beside the 12 volt cig plugs. Like the FJ?